stale_mongos_and_restarted_shards_agree_on_shard_version.js has a test-only bug where if the insert at line 135 fails, then later abortTransaction at line 139 will throw, crashing the test. This is due to the fact that the insert() at line 135 doesn't throw on error, but instead returns, so the error is ignored, and later a somewhat complex interaction ends up with the unhandled exception (see comment in BF-35416).